Typically the life of a vehicle depends on many different variables such as if it is driven highway or city, if it is regularly maintained, garaged or non-garaged, and varying driving styles from person to person. With that said, the Toyota Sienna Minivan has had its issues since its 1998 beginnings. To start there is a known problem with engine sludge that can cost you the engine, literally I read about a guy that started having problems within 3 months of purchasing a new Sienna and the motor was gone at 25,000 mi 2 years later (http://philip.greenspun.com/materialism/cars/sienna in the comments first one). People have complained about poor design quality and oversight on Toyota engineering. There are Siennas on the road on the other hand that have lasted 350,000+ miles and are still going strong. I would say you should be able to expect 100-150,000 miles reasonably on a Sienna after that will most likely depend on maintenance, driving/weather conditions, and a bit of plain old luck.